The present invention relates to a valve disposed in an exhausting line of an evacuation device such as a CVD (Chemical Vapor Deposition) device in order to stop/start exhausting gas flow and to control evacuation conductance automatically. More particularly the present invention relates to a widely variable conductance valve driven with an electric motor which is applicable to controlling of process gas in a semiconductor fabrication process using a reduction pressure CVD device, for example.
To describe an evacuation device where a valve of the present invention may be used, function of a valve will be described below referring to a major semiconductor fabrication device, for example.
FIG. 1 generally illustrates a device applicable to system of semiconductor fabrication such as a reduction pressure CVD device.
The reference sign A depicts an evacuation pump, B depicts a variable valve, and C does a reaction chamber where a work to be processed is placed. The reaction chamber C is connected with a process-gas supply E through a mass-flow controller D. The reference sign F depicts a vacuum gauge for monitoring pressure in the reaction chamber C. A pressure signal detected by the vacuum gauge F is transmitted to an automatic pressure controller G to be compared with a predetermined pressure signal so as to output a drive signal for adjusting an opening degree of the variable valve B. The drive signal adjusts the opening degree of the variable valve so that the pressure in the reaction chamber C is controlled to be the predetermined pressure. Further, the reference sign H is a heater for heating the reaction chamber C.
A silicon wafer I to be processed is placed in the reaction chamber C which is connected with the process gas supply E, and the valve B is opened to evacuate the reaction chamber C down to a target pressure, about 0.5 Pa. Then a process gas such as NH.sub.3 (ammonia) is introduced into the reaction chamber C from the process-gas supply E via the mass flow controller D so as to regulate the opening degree of the variable valve B to be a predetermined pressure, about 133 Pa, monitoring the pressure in the reaction chamber C with the vacuum gauge F. Upon supply of the process gas and suction of the gas by the evacuation pump A via the valve B, the silicon wafer I is deposited under the predetermined pressure of the process gas. During the process the reaction chamber is controlled by the opening degree of the valve B to be at the predetermined pressure. Further, on completion of the process, the introduction of the process gas is stopped, and the valve B is fully opened to evacuate the reaction chamber C to the target pressure. The variable valve B is then fully closed to increase the pressure in the reaction chamber C up to the atmospheric pressure, thereby taking finished products out of the chamber.
FIG. 2 exemplifies a conventional variable valve used in the above device.
The reference numeral 101 depicts a throttle valve body having a flange portion 101b circumscribing a fluid passage 101a. The numeral 102 is a disc-shaped valve body having almost the same diameter as that of the fluid passage 101a of the throttle valve body 101, and the valve body 102 is openably mounted at the fluid passage 101a. The reference numeral 103 depicts a drive shaft for connecting the valve body 102 with a valve drive portion 104. The drive shaft 103 is connected with the valve body 102 by means of a pin 105 so as to turn integrally with the valve body 102. A drive means within the drive portion 104 turns the drive shaft 103 to rotate the valve body 102 and change an opening area of the fluid passage 101a.
As mentioned above, during the process the pressure in the reaction chamber C must be controlled within a wide range from the atmospheric pressure (1013 HPa) to a few Pa. Further, a pressure around the few Pa, the lowest limitation of the range, must be finely controlled. In the conventional variable valve which is a throttle valve, the valve body 102 may be turned to control the process gas to be a few Pa but cannot prevent leakage when fully closed because of its structure. On completion of the process, the pressure in the reaction chamber C is brought to the atmospheric pressure. Thus, even if the valve is fully closed, the valve is not able to be completely isolate the reaction chamber C from the evacuation pump A. Therefore an isolating means has been separately needed.
Most process gases used in semiconductor fabrication liquefy at an ambient temperature. When a process gas is cooled down, it may be deposited on an inner wall of a device. It may also be deposited on outer surfaces of the valve body or inner surfaces of a flange. As such deposition increases, an appropriate adjustment of an opening degree may not be completed. In the worst case, the valve body would not move to open or close. Then, such a throttle valve is disassembled to clean its valve body, inner surface of flange etc. However such disassembling and cleaning is troublesome. Further, most of process gases are toxic and dangerous, and care should be taken to handle these process gases. Such a conventional valve may have heaters on at a valve body and a flange portion to prevent deposits of materials, whereby simplifying such device and decreasing the number of components.